1. Field of the Invention
The present invention to relates to the field of ground plates, and more particularly to a ground plate for a photosensitive drum and improvements thereto.
2. Description of the Related Art
Photosensitive drums for use in image forming devices such as copying machines, facsimile machines, and printers are well known in the art. A typical photosensitive drum includes a hollow metal cylinder having an organic or non-organic photoconductive layer on the outer surface and a pair of end caps, as disclosed, for example, by U.S. Pat. No. 5,729,792 to IKEHARA et al., U.S. Pat. No. 6,006,053 to IKEHARA, and U.S. Pat. No. 5,943,527 to KASHIWAGI et al. The typical photosensitive drum assembly also includes a nonconductive flange inserted in each end of the photosensitive drum, a support axle passing through the drum via apertures in the flanges, and a ground plate attached to the inner surface of one or both of the flanges.
The prior art also includes a photosensitive drum cartridge, as disclosed, for example, by U.S. Pat. No. 4,839,690 to ONODA et al. This drum cartridge includes a hollow metal cylinder having a photosensitive layer, a pair of resin flanges inserted in the ends of the cylinder and a pair of positioning pins or drum shafts for supporting the drum cartridge, and a conductive plate attached to the inner surface of one of the flanges. A leaf spring portion of the conductive plate contacts the end face of one of the positioning pins.
A disadvantage of the prior art is the complicated nature of the ground plates. The prior art ground plates have particularly intricate and complicated shapes that are difficult to manufacture. Additionally, the manufacture of some of the prior art ground plates also includes several steps after cutting or stamping since the contact members for the ground pin must be folded back toward the center of the ground plate following the cutting or stamping of the ground plate.
Another disadvantage of the prior art is the disc shape of the prior art ground plates. The disc shaped ground plate consumes unnecessary material. Acceptable electrical contact to provide high quality grounding does not require that the entire end cap be covered. Therefore, it is not necessary to form the ground plate in a disc shape and waste valuable material. Another disadvantage of the disc shape of the prior art ground plate is that it is dangerous to handle. The disc shaped ground plate of the prior art includes projections about the entire circumference of the ground plate. The projections are very sharp in order to scratch the inner surface of the photosensitive drum. Therefore, sharp projections extend from the entire edge of the ground plate, and it is extremely difficult to quickly find a safe spot to grasp when handling the ground plate. Many handlers of such ground plates have been injured.
The present invention is directed to a ground plate for a photosensitive drum in an image forming device, which addresses the problems existing in the prior art, discussed above.
An aspect of the present invention provides a ground plate for a photosensitive drum assembly, including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of a photosensitive drum in the photosensitive drum assembly to make electrical contact between the ground plate and the photosensitive drum. The legs may extend in directions substantially parallel to each other. Further, each of the projections may extend in directions substantially parallel to each other.
According to a further aspect of the present invention, the plurality of legs may include four legs, and the central portion and the four legs may substantially form an H shape. Further, each of the legs may include two projections extending therefrom to scratch the inner surface of the photosensitive drum, and the projections may extend out of the plane of the substantially planar member.
In a further aspect of the present invention, the substantially planar member may include a two piece construction. The substantially planar member may further include a first leg and a second leg, each of the first leg and the second leg including a spring contact extending from a central portion thereof, the first and second legs being spaced from each other to secure a ground pin therebetween when fixed to an end cap. The ground plate may farther include a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives a ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin. Further, the ground plate may include two spring contacts. The ground plate may further include a plurality of apertures provided in the substantially planar member, each of the apertures being configured to receive a protrusion on an end cap of the photosensitive drum assembly, and a plurality of projections provided in each of the apertures, the projections being configured to engage the protrusions on the end cap of the photosensitive drum received in the apertures and to fix the ground plate to the end cap of the photosensitive drum.
A further aspect of the present invention provides a photosensitive drum assembly for an image forming device including a photosensitive drum, the drum including a photosensitive layer on an outer surface thereof, a first end cap and a second end cap, the end caps being configured to fit into the ends of the drum, and a ground plate fixed to an inner face of the first end cap, the ground plate including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of the photosensitive drum to make electrical contact between the ground plate and the photosensitive drum. The photosensitive drum assembly may further include a ground pin extending through an aperture in the first end cap, and the ground plate further including a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives the ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin.
Another aspect of the present invention provides an image forming device including a printer engine, and a photosensitive drum assembly mounted in the printer engine, the photosensitive drum assembly including a photosensitive drum including a photosensitive layer on an outer surface thereof, a first end cap and a second end cap, the end caps being configured to fit into the ends of the drum, and a ground plate fixed to, an inner face of the first end cap, the ground plate including a substantially planar member, the substantially planar member including a central portion, and a plurality of legs extending from the central portion, at least one projection extending from each of the plurality of legs, each of the projections being configured to scratch an inner surface of the photosensitive drum to make electrical contact between the ground plate and the photosensitive drum. The image forming device may further include an engine frame, a spring ground contact mounted on the engine frame, the photosensitive drum assembly further including a ground pin extending through an aperture in the first end cap, the ground plate further including a central aperture in the central portion, and a plurality of spring contacts extending into the central aperture, wherein the central aperture receives the ground pin therethrough and the plurality of spring contacts engage the ground pin to make electrical contact between the ground plate and the ground pin, and wherein the ground pin is configured to contact the spring ground contact to make electrical contact between the ground pin and the spring ground contact to ground the photosensitive drum.